While perusing Hayao Miyazaki's profile on IMDb I came across a cartoon series he directed in 1978, pre-Studio Ghibli. After getting a package from a couple oceans over, we watched a few episodes in movie club. Based on Alexander Key's 1970 novel The Incredible Tide, Conan and his grandfather live alone on an island twenty years after a megabomb destroys most of Earth, not knowing if they're the sole inhabitants or not. Things get interesting when a young woman washes ashore, followed by other visitors.
If you're a fan of Miyazaki's other work, it's definitely worth checking out.